Spell check is an optional setting that will highlight any misspelled words when composing a message and offer up to three suggestions for replacing that word.
NOTE: Must be on LightOS v312 or later for Spell-Check feature.
When a word is misspelled, an underline appears in the compose message screen.
To view suggested spellings, long press the underlined word, which will hide the keyboard and display up to three alternatives.
Enabling/Disabling Spellcheck
To toggle on or off the spellcheck setting go to:
Settings > Preferences > General > Keyboard: toggle "Spell-Check"